Quick moldmaking question.

[evaldart]

Hey brothers and sisters of goo goop and glop. I am in the process of making a latex mold but before I begin slopping the stuff on (the 12-14 required coats) I noticed that there was no mention of any different requirements whether it goes over oil based or water based clay. I am going over water based clay (typical variety) and the sculpture is just at leather hard (aside from the aswipes and smudges of wet clay that I filled-in some drying-crackage). The can says that there is no prepping or release-agent necessary (I'm using Environ-Molds products - Summit NJ). It will be a two piece mold - but the relative hardness of the clay combined with the bulk of rigid armature could make the de-molding a bit nasty.

Any advise? Thanks

[Andrew Werby]

I'd give it a coat of a dishwashing liquid, like Joy or Dove and let it dry before applying the first layer of rubber. It won't hurt the latex and it will help it release. Don't use Vaseline, whatever you do - that will rot the latex.

Andrew Werby
Juxtamorph.com

[evaldart]

Will-do...thanks A.W.

[evaldart]

Oh, and has anyone got a common substance that would suffice as a thickener in the later coats (as I forgot to order the "offcial" version from the company...and this is due immediately).?

All this will be supported by a regular plaster mother mold...just wondering if I could save some steps and make it a paste with something...spackle instead of brush..

[Robson Valley]

In a past life, there was a product called "glove powder". Think it was no more than an unscented talcum powder. Would be a good filler.

Try a store that sells commercial diving equipment. I worked for 5 months in a dry suit in water as cold as 4C/40F. Getting my fat head past the neck seal took a lot of powder!

[evaldart]

Talc...yes. Thanks.

[obseq]

Originally Posted by evaldart

Oh, and has anyone got a common substance that would suffice as a thickener in the later coats (as I forgot to order the "offcial" version from the company...and this is due immediately).?

All this will be supported by a regular plaster mother mold...just wondering if I could save some steps and make it a paste with something...spackle instead of brush..

I've used completely frayed/undone twine for plaster mother molds in the past with success.
It's cheap and really easy to toss in there to use.

[ironman]

ASTROGLIDE!!!!!!!!!!

[Andrew Werby]

I think Astroglide is based on silicone oil, which will weaken silicone rubber. And while adding powders to your rubber will thicken them, it also makes them weaker and more liable to tear. The Part C thixotrope you forgot to order works a lot better. Maybe FedEx?

Andrew Werby
www.computersculpture.com

[evaldart]

Yeah, I usually use the fumesilica stuff. But this mold wont be used much. It is going to the foundry where they are going to do their own thing with it...its a one-shot project...not an edition.

[obseq]

What did you end up doing with this mold, E?

[Owen Weng]

Andrew, that's a good tips.The dishwashing liquid also works as a separator which can make the further de-modeling process easier.

Originally Posted by Andrew Werby

I'd give it a coat of a dishwashing liquid, like Joy or Dove and let it dry before applying the first layer of rubber. It won't hurt the latex and it will help it release. Don't use Vaseline, whatever you do - that will rot the latex.

Andrew Werby
Juxtamorph.com

[luna]

Interesting train of thought and tips, but why latex in the 1st place? Urethane or silicone is so much more manageable, (3 coats in either, depending on the product, would easily give you the thickness of 15 coats of latex, and latex shrinks! pulls out of concaves.) You would need to seal the water-based clay, but if a mold is your goal, you would be better off modeling in a non sulfur oil based clay to begin with.

Anthony Tafuri
www.tafuristudios.com

[Richard Smith]

I like to use fiberglass window screen in my later layers. Cut it up into usable squares and imbed it into wet latex/rubber. Then back fill with another layer of wet stuff. If you overlap the screen pieces the mold becomes really tear resistant. Also the screen stiffens the rubber up a bit so it sits better into the shell. And this is a caveat emptor, you can cut down on the number of layers of latex you have to use but make sure you don't get too carried away.
Rich

[raspero]

Richard,

That sounds like a solution to what may be my most aggravating mold problem: the rubber wanting to sag down as I rotate the mold while pouring the wax. The alternative, much thicker rubber molds, is pretty pricey.

Thanks.

[Mack]

One thing I've done in my last molds which were fairly large, in order to keep the rubber from falling away from the mother mold is to pour some small rubber cylinders(I used the center of a small metal wire spool for the mold) slice them up and attach them to the last coats of rubber in strategic places. Then when I brush on the plastic resin that I use for the mother mold, I keep the top of the rubber cylinders (teats) clean and flush with the finished surface of the mother mold. Then when I put the rubber mold back into the mother after removing the original model, the rubber cylinders poke through the mother and hold the rubber mold in place and the friction helps keep it from sagging. The cylinders or teats that I used were about 3/4" wide and a half inch high.

[raspero]

Thanks Mack. I will try that for sure.

R

[Dries]

Glass marbles placed strategically on the outside layer of the inner mould and covered up to +-3/4 with rubber or silicon works very well. When the mould cured completely you just remove the marbles and let the mother mould fill the voids, now you can snap the inner mould onto the mother mould. I think this tip was given to me by someone in this forum and if been using it ever since.

[raspero]

I love it. That makes perfect sense. One of those, "It's so obvious how could I not have thought about it ages ago?" But didn't of course.

Richard

[luna]

Dries has a good point with marbles to lock in, I often use rubber stoppers, available in any hardware store, and provide many sizes and no undercuts to start with. I still suggest, though, like my previous post...use urethane for low cost molds...thick, quick, good longevity and excellent detail.